textproduct: Quad Cities

KEY MESSAGES

- Dense fog is possible again tonight into Saturday morning.

- A strong system to affect the area later in the weekend, first with showers and for along and south of I-80 even t-storm potential (20-30%) Saturday night through midday Sunday.

- The system will then bring a chance of snow, but more so windy and much colder conditions Sunday afternoon and night into early Monday, with gusts potentially nearing 45 mph and wind chills of 0 to 15 below zero likely to start Monday.

SHORT TERM /THROUGH SATURDAY/

Issued at 300 AM CST Fri Dec 26 2025

Another cloud-filled start to a day which will continue to be a theme for a few more days. Fog is again a problem with temporary reduced winds under the passage of a 1003 mb low pressure center and residual boundary layer moisture trapped below a stout inversion as sampled on last evening's sounding (5C increase between 1 and 2 kft AGL). Some of this fog per webcam and visibility observations is quite thick (few hundred yards or less), and with advection fog in the wintertime is not surprising.

On the backside of the low's passage between 7 and 10 AM, a strengthening pressure gradient will allow for west-northwest winds to quickly uptick to 10-15 mph. Upstream across the western half of IA and northwest MO, this has allowed visibility to improve. So envision a southwest to northeast improvement in visibility during that few hour window. Some tweaks to the Dense Fog Advisory area and timing very well may be needed though, including in the far south where mixing in the warm sector has already allowed for some improvement.

Clouds will be slower to improve than visibilities today, and as the previous AFD stated, any sun might be quite transient and probably limited to south of I-80 if it occurs. Through late morning, the stratus will still be deep enough that patchy drizzle may continue. The stratus will also mean a low diurnal range, with any warming offset by the northwest winds, resulting in "steady temperatures" being a reasonable forecast for today.

For tonight into Saturday, more of the same with continued clouds and probable lower diurnal ranges than what the NBM indicates. Have adapted that into the forecast. Could be some fog tonight just due to residual moisture, but we should not be in as favorable of environment for an existing stratus deck to lower to the ground such as in recent nights.

LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/

Issued at 300 AM CST Fri Dec 26 2025

The system of interest for later in the weekend is actually a phasing of two systems -- a stronger one near the CONUS border and a more subtropical jet-rooted one. Most deterministic models agree with a phasing in the Midwest to Great Lakes region. With a fairly wide open Gulf and an existing baroclinic zone in the region, warm and moist advection Saturday night should result in a regional increase in isentropic ascent and showers. This is supported in the end of CAM solutions. The low-level warm advection will allow for CAPE to likely expand into at least the southern CWA, with available ensemble probabilities of MUCAPE exceeding 200 J/kg of around 50%. Also noteworthy is a tight gradient in low-level based CAPE exceeding 100 J/kg near the southern CWA edge Sunday morning. Continue with the chance of thunder in that area, but with the kinematics and where the low-level CAPE/shear spectrum is with respect to climatology (as shown by ECMWF EFI), will also have to watch for convective induced wind potential in the southern and far eastern CWA. As noted in the previous AFD, precipitable waters are forecast AOA one inch in the southern CWA (near late December maxes on climatology), so temporary heavy rain rates could occur, but quick cell movements and ground conditions should not yield notable hydro issues. One final note for Saturday night/Sunday morning, is for any area that see less showers, there could be dense fog again given similar dew points to this morning.

With a projected deepening of the system favored to our east Sunday afternoon into night, that means a strengthening pressure gradient in tandem with cold air advection. The isallobaric influence and the strongest top of the channel winds look to maximize Sunday evening into overnight, and during that period have collaboratively gone with NBM's upper quartile sustained winds of around 25 mph, with gusts probable (50-80%) to exceed 40 mph. These probabilities drop off for gusts over 45 mph, but looks to be at least close to Wind Advisory criteria.

Forcing for precipitation within the cold air advection looks to still be present Sunday P.M. through Sunday night and possibly even into Monday morning when the upper trough swings over or just north of the area. So this provides forecast snow chances, but over how much of the area and how impactful are uncertain. Conceptually, the forecast path of the system would favor north of I-80 for snow chances, and the NBM membership does have 30-50% probabilities of snowfall > 1 inch in this area for Sunday afternoon through Monday morning. With milder pavement after this prolonged above freezing stretch, road impacts may be limited even if snow does materialize. Predictability of this ~60 hours out is still on the lower end.

Confidence is high in temperatures being 30 to 35 degrees colder Monday morning than Sunday morning as temperatuers in the upper single digits to teens start the last Monday of 2025. Attendant wind chills are presently forecast in the zero to 15 below zero range. While not to Cold Advisory criteria level, it will be a bit harsh of a snap back to reality. While some moderation already midweek, temperatures look to stay at to below normal for at least a few days.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 1148 AM CST Fri Dec 26 2025

Predominantly IFR/LIFR conditions expected, with some lower MVFR (ceilings) possible near MLI/BRL this afternoon and then some potential for LIFR/VLIFR becoming more widespread again tonight in fog/low clouds.

Visibilities will continue to gradually improve through this afternoon due to a combination of weak cold advection and strengthening NW surface winds occasionally gusting to around 15 kts. There is an overwhelming consensus signal in the guidance for widespread LIFR/VLIFR conditions developing again tonight into Saturday morning. Latest HREF probabilities of < 0.5 mile grow to 50-70% by 12z Saturday. There is some uncertainty as to whether this may be more stratus and not as much fog given the setup being not as favorable with a NW wind and slight dry advection. However, later tonight into Saturday morning, as the winds go light and then shift from the southeast back to moist advection that's when we may see more widespread LIFR/VLIFR and have trended toward this idea in the TAFs.

DVN WATCHES/WARNINGS/ADVISORIES

IA...None. IL...None. MO...None.